Well, there are Teramin presets available for some soft synths - cannot recall which, but likely candidates might include Reaktor or Kontakt. Please note that which synths have those types of sounds is conjecture.
The reason I mention it is that you can pick up any number of inexpensive midi controllers, and several bands I am aware of play live music that is aided by sequenced keyboard parts. Please note that it takes a great deal of discipline to do so, as the tempo of whatever is playing in the computer is quite unwilling to change to match any variance in tempo from the band.
But on the positive side, doing so would enable your band to have an inexpensive keyboard player, in addition, someone could play rudimentary keyboard chords/leads live using sounds triggered from the controller.
Of course, the same option is there if you find a keyboard with its own local sounds in your price range.
Anyways, hope you work it out.
Bob Bone